Downhole drilling motors are used to power the drill bit during certain well drilling operations, such as where the direction of a well bore needs to be changed rather abruptly and with precision in order to reach a desired earth formation target. Such motors generally are powered by the circulation of well drilling fluid, commonly called drilling "mud", that is pumped from the surface down through the drill pipe where the fluid exits through the nozzles or jets in the drill bit and then returns to the surface through the annular space between the borehole wall and the drill pipe. Of course the fluid lubricates and cools the bit and carries rock cuttings up and out of the well. Drilling motors have taken various forms such as turbines, rotating vane devices and Moineau motors. However, all the designs that applicant is familiar with have not had a very long useful life due to the extremely rugged service conditions that are encountered. A principle factor in early breakdown is due to the fact that the drilling fluids even after filtering at the surface contain small abrasive rock particles that cause rapid wear of various motor parts, particularly the rotating shaft seals and bearings that typically are present in a motor assembly. The problem will be readily appreciated when it is realized that in all fluid driven motors of the types described above, the pressure drop across the bit nozzles causes the drilling mud with entrained rock particles passing through the motor to enter the seals and bearings, which leads to abrasion and wear of seal surfaces and damage to the elements themselves. Of course, the motor substantially inoperative for continued well drilling operations due to rapid leakage of fluids to the annulus with consequently reduced horsepower output, and even shaft seizure, so that the motor can no longer function to drive the drill bit efficiently (or perhaps even at all). When failure occurs, the drilling operation must be terminated and the drill pipe and the motor withdrawn from the well so that the motor can be replaced or repaired, which is a time consuming and thus costly procedure.
The maintenance of operative rotating shaft seals and bearings has continued to be a vexing problem that has limited the use of downhole drilling motors as effective well drilling tools. It is to a unique solution to this problem that the present invention is directed.
The general object of the present invention is to provide a new and improved rotating shaft seal or bearing apparatus that is designed for the very rugged service conditions such as may be encountered, for example, in well drilling operations using a downhole motor.